High-precision female format multifiber connector

ABSTRACT

A female format connector, usable for connection with a male format connector having an alignment pin is described as having a high-precision piece coupled to a low precision piece. The low precision piece has an alignment opening dimensioned to accept the alignment pin of the male format device. The high-precision piece also has an alignment opening. The alignment openings are sized and positioned for accurate alignment between the pieces during coupling and, after coupling, the high-precision piece is modified such that the second alignment opening, after modification, is larger than it was prior to the coupling. A method of forming a female format ferrule involves coupling a high precision piece to a low precision piece, via alignment holes on each, the alignment holes are sized to accept a common alignment pin for maintaining accurate alignment between the pieces during coupling, and, after coupling, removing some of the alignment hole wall.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly assigned U.S. patentapplication Ser. No. 10/098,652, (now U.S. Pat. No. 6,609,835), Ser. No.10/098,255 now U.S. Pat. No. 6,619,855 and Ser. No. 10/098,990 (now U.S.Pat. No. 6,629,780), all filed Mar. 14, 2002 which arecontinuations-in-part of commonly assigned U.S. patent application Nos.09/896,513, 09/896,664, (now U.S. Pat. No. 6,773,166) Ser. No.09/896,196 and 09/896,192, all filed Jun. 29, 2001 and which are allincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to components and processes for fiber opticrelated component fabrication. More particularly, the invention relatesto the fabrication of optical coupling and waveguiding elements.

BACKGROUND OF THE INVENTION

Optical Fibers in commercial systems have been traditionally held byusing a combination of pieces.

A connector assembly 100, such as shown in FIG. 1 as an exploded view isused to attach various fiber pieces (or fiber pieces and modules)together. A ferrule 102 is the part of the connector 100 into which thefibers 104 themselves are inserted before the ferrule 102 is insertedinto the overall connector itself. The ferrule 102 is a ‘high-precision’piece of the assembly 100. It holds the fiber(s) 104 in a preciseposition and ensures that when two connector pieces are attached, thatthe fibers in the two pieces are held in accurate alignment. Theremainder of the connector 106 is ‘low precision’ relative to theferrule 102.

In the multi-fiber connectors available today, most of the connectionsare for fiber arrays of 2 or more fibers, such as shown in U.S. Pat. No.5,214,730, up to arrays of 1×12 (although some commercial 2×12configurations have been tried). The connectors employed are referred toby various names depending upon who makes them. In 1×2 arrays,connectors are referred to as ST, LC, MT-RJ connectors while for 1×12arrays the connectors are referred to as MTP®, MPO, MPX and SMCconnectors, among others. In the 1×12 or 2×12 area, all of the variousconnectors use a common type of ferrule commercially available from,among others, US Conec Ltd. and Alcoa Fujikura Ltd. In addition,commercial connectors for small arrays (less than 12) fibers have alsobeen proposed, for example, in U.S. Pat. No. 5,743,785.

Fiber holding pieces, such as ferrules 102, can be made by moldingplastic or epoxy pieces containing holes 108 into which optical fibers104 can be inserted. Fibers must be able to be centered in each holeprecisely and repeatably.

When an array of holes is made in a material for holding optical fibers,there are two aspects which need to be controlled. The spacing betweenholes (the “pitch” of the holes) and the diameter of each hole. Bothhave some margin of error due to the inherent inaccuracies of thefabrication techniques. If inaccuracies introduce errors in either (orboth) pitch or size that are too large, then the fibers can be insertedat an angle or will not be positioned correctly in the ferrule. Ineither case, this negatively affects the ability to couple lightefficiently, if at all, from one bundle to another or from an optical oropto-electronic component to a fiber bundle. If the hole pitch isinaccurate, then fibers from one bundle will not line up well withfibers of another bundle. However, even if the center-to-center pitch ofthe holes is very accurate, because the hole diameter is larger than thefiber (and each hole likely varies across an array) each fiber need notbe in the exact same place in the hole as the other fibers in theirholes, then that can cause misalignment, leading to inefficiencies orunacceptable losses. For example, if each of the holes in a ferrulepiece was accurate to within 4 microns, then adjacent fibers could beoff in pitch by up to 4 microns, since one fiber could be pushed to oneside by 2 microns and the adjacent fiber could be pushed in the otherdirection by 2 microns. While this may be acceptable for multi-modefibers, for single mode fibers this would be a huge offset that couldmake connections unacceptable or impossible.

In addition, fibers should generally not be placed in a hole at an angleor, if inserted at an angle, the particular angle should be specificallycontrolled.

FIG. 2 shows an example connector hole 200 and fiber 202. The innercircle, represents an actual fiber 202 while the outer circle,represents the hole 200 in the ferrule. As shown, the difference insizes is not to scale but is exaggerated for purposes of illustration.Nevertheless, in actuality, the ferrule hole 200 must be larger than thefiber 202 by enough of a margin to allow for easy insertion—ultra-tighttolerances can not be effectively used. While the fiber 202 shouldideally be centered with respect to the hole 200, as can be seen in FIG.3, any individual fiber 202 could also be pushed in any hole 200 tosomewhere else in the hole, for example, either the left or right edge(or any other edge) where it would not be centered within the hole 200.Thus, even if the ferrule has an accurate pitch “P” between hole centers204, adjacent fibers 200 in an array may have an incorrect pitch “P+2ΔP”due to the offset ΔP between the center 206 of each hole 200 and wherethe fiber 200 lies within the hole 200, in this case, causing anincorrect pitch of P plus 2 times the individual offset ΔP in each hole.

The 1×12 and 2×12 ferrule technology currently in commercial use isbased upon a glass filled epoxy resin (a high-performance plastic) whichis fabricated using a common plastic molding technique called transfermolding. Today, ferrules molded out of epoxies or plastics can be madeto the necessary tolerances for multimode fibers, but special care mustbe taken during fabrication. Plastic molding technology is very processsensitive and molds having the requisite precision are extremelydifficult to make. Even so, yields tend to be poor due to the inherentmanufacturing process errors that occur in plastics molding. Since thetolerances on these pieces must be very accurate (on the order of about1 to 2 micrometers), high yield manufacture is difficult. As a result,the cost of terminating fiber bundles into these connectors can be quiteexpensive, running hundreds of dollars per side. In addition, theprocess is not scalable to larger numbers of fibers (particularly 30 ormore) because of inaccuracies and yield issues associated with moldingtechnology and reliable production of ferrules for similar numbers ofsingle mode fibers is even more difficult.

There has been an increasing need among users in the fiberoptic fieldfor larger groups of fibers, so demand for connectors to handle thesegroups has been increasing as well. As a result, creation of connectorsfor larger arrays, such as 5×12, have been attempted. One manufactureris known to have made a 5×12 connector array, but achieved such pooryields that they deemed an array of that size unmanufacturable.Moreover, the cost of producing the pieces resulted in their being soldfor $500 each, due to poor yield, and the mold for producing the pieceswas destroyed during the process.

The problem is that in plastic molding pieces for holding higher fibercounts in small spaces results in less structural integrity for themolded piece. As such, the prior art has been forced to do withoutcommercial connectors for such large arrays, because 5×12 arrays can notbe reliably created and commercial connectors for larger format arrays(e.g. even a 6×12) are considered prohibitively difficult to evenattempt.

The ferrule area is very small, since ferrules for the above MTP, MPO,MPX or SMC connectors are about 0.07″ high, 0.3″ wide and 0.4″ deep, somolding or machining of features in the ferrules of the sizes requiredto hold multiple optical fibers (which typically have about a 125 microndiameter for a multimode fiber and a 9 micron diameter core for a singlemode fiber) is very difficult. Since single mode fibers have an evensmaller diameter than multimode fibers, molding or machining ferrules toaccommodate large arrays of single mode fibers is currently, for allpractical purposes, impossible—particularly on a cost effectivecommercially viable scale.

Additionally, making ferrules for arrays is made more difficult due toprocess variations during production because, as the holes approach theedge of the ferrule, the structural integrity of the walls decreasecausing parts to have poor tolerance at the periphery, become overlyfragile causing component collapse in some cases, or prohibiting removalof material from the inside of the piece that impedes or prevents fiberinsertion.

Some have attempted to make two-dimensional fiber bundle arrays bycreating a dense packing of fibers together, for example, as describedin U.S. Pat. No. 5,473,716, and K. Koyabu, F. Ohira, T. Yamamoto,“Fabrication of Two-Dimensional Fiber Arrays Using Microferrules” IEEETransactions on Components, Packaging and Manufacturing Technology—PartC, Vol 21, No 1, Jan. 1998. However, these attempts have not yielded asolution, particularly for the types of connectors mentioned above,because the inaccuracies of fiber production result in diameters offibers which fluctuate within a 2 micron range (i.e. plus or minus 1micron). Hence if 12 fibers are stacked in a row, there could be as muchas 12 microns of inaccuracy in fiber alignment. Even with multi-modefibers (the best of which use 50 micron cores), a misalignment of 12microns will cause unacceptable light loss for most applications. Forsingle mode fibers, which typically have 9 micron diameter cores, a 7 to12 micron misalignment could mean that, irrespective of the alignment ofthe fiber at one end of the row, entire fibers at or near the other endof the row could receive no light whatsoever. For two-dimensional fiberarrays, the problem is even worse because the inaccuracy of the fiber isnot limited to one direction. Thus, for example with a 16×16 array, aplus or minus 1 micron inaccuracy could result in fiber misalignments byup to 23 microns or more. Compounding the problem is the further factthat fiber inaccuracies stated as plus or minus 1 micron do not meanthat fiber manufacturers guarantee that the fiber will be inaccurate byno more than 1 micron. Rather, the inaccuracy statement represents astandard deviation error range. This means that most of the fiber shouldonly be that inaccurate. Individual fibers, or portions thereof, couldhave larger inaccuracies due to statistical variations.

As a result, the larger the number of fibers, the more likely a problemdue to fiber inaccuracy will occur because, for example, using the 16×16array above, the array would have 256 times the chance (because thereare 16×16=256 fibers) of having at least one of these statisticallyanomalous fibers in the group.

Others have attempted to align two dimensional arrays of fibers (e.g.4×4 arrays) in a research setting, but none have applied theirtechniques to conventional connector technologies. Moreover, thetechniques are not suitable or readily adaptable for high yield, lowcost, mass production as demanded by the industry. For example, somegroups have examined the use of micromachined pieces made out ofpolyimide as described in J. Sasian, R. Novotny, M. Beckman, S. Walker,M. Wojcik, S. Hinterlong, “Fabrication of fiber bundle arrays forfree-space photonic switching systems,” Optical Engineering, Vol 33, #9pp. 2979-2985 September 1994.

Others have attempted to use silicon as a ferrule for precisely holdingfiber bundle arrays since silicon can be manufactured with very highprecision (better than 1 micron) and techniques for processing ofsilicon for high yield is, in general, well understood.

Early attempts at silicon machining for two-dimensional array fiberplacement were performed with some limited success and one-dimensionalfiber arrays, using fibers placed in V-Grooves etched into a piece ofsilicon, have been created, for example, as shown in FIG. 4A. Theapproach used the silicon pieces to hold the fibers but no attempt wasmade to integrate such an arrangement into a commercial connector.

Other groups took the V-Groove approach of FIG. 4A and performed anexperiment where they stacked two of pieces together FIG. 4B forinsertion into a connector. This resulted in a minimal array with tworows of fibers, as described in H. Kosaka, M. Kajita, M. Yamada, Y.Sugimoto, “Plastic-Based Receptacle-Type VCSEL-Array modules with Oneand Two Dimensions Fabricated using the self-Alignment MountingTechnique,” IEEE Electronic Components and Technology Conference, pp.382-390 (1997), but the technique was not scalable to larger formattwo-dimensional arrays, such as shown in FIG. 4C.

Still other groups looked at holding larger format two-dimensionalarrays using silicon pieces machined using wet-etching techniques, asdescribed in G. Proudley, C. Stace, H. White, “Fabrication of twodimensional fiber optic arrays for an optical crossbar switch,” OpticalEngineering, Vol 33, #2, pp. 627-635, February 1994.

While these silicon pieces were able to hold fibers, they were notdesigned to be, and could not readily be, used with existing ferrule orconnector technology. Moreover, they could not be used for single modefibers with any accuracy.

Thus, none of the above attempts have provided a viable solution to theproblem of how to effectively create a large format fiber array which:allows for high precision holding of large arrays of fibers, especiallysingle mode fibers, is compatible with current commercially usedconnectors that attach two fiber bundles to each other or one fiberbundle to a component containing an array of optical devices, such aslasers and/or detectors, and that allows for easy fiber termination in arapid fashion at low production cost.

In addition, because of the above problems, there is presently no largeformat ferrule apparatus that can maintain fibers at a low angle, or ata precisely specified angle, for good optical coupling.

Collimating arrays are conceptually arrays of pipes for light. Massproduction of collimating arrays for commercial applications has largelybeen dominated by the digital photographic camera and digital videocamera world. These applications typically use a device called a“faceplate”, which is a multi-fiber assembly used to direct light ontooptical detectors used for imaging. Since, for cameras, effectiveimaging requires the maximum amount of light reach the detectors, afaceplate will have several fibers per individual detector. In fact, inthe most desirable faceplates, the number of optical fibers exceeds thenumber of optical detectors by many times. Thus, light being directed toa single detector in such a camera passes through multiple opticalfibers arranged in parallel, and a camera has one detector per pixel.For imaging systems like cameras, this collimating technique issufficient to accomplish its purpose. However, when dealing with opticalcommunication systems, faceplates can not be used because the light lossresulting from such a collimating arrangement is significant. Thefaceplate technique (sometimes also referred to as oversampling) is alsoincompatible with the use of single mode fibers or lasers (which arehighly desirable for use in high speed, long distance datatransmission). Hence, the collimating technique of using a faceplate,such as made for use in cameras, is an unworkable approach foropto-electronic communication devices.

As noted above, for one-dimensional optical device arrays, attempts havebeen made to create collimators by using a piece of silicon wafer, intowhich V-Grooves are etched, and laying the fibers into the V-Grooves asshown in FIG. 4A. This is an operational approach for forming aone-dimensional array that is unsuitable for mass production.

Other groups have attempted to stack multiple V-Groove arrays on top ofone another (FIGS. 4b, 4 c) to create a larger collimating element.Unfortunately, the accuracy of stacking in the second dimension islimited by the accuracy of the thickness of the individual wafers, bothon an absolute basis and on a relative basis, due to thicknessvariations over the area of the wafer. In addition, the stacked V-Groovetechnique requires such accuracy that individual stacks must beindividually built up one at a time; a costly and inefficient process.

Similarly, optical waveguides are also conceptually pipes for light.Presently, there are also no inexpensive two dimensional opticalwaveguide combiners available for commercial applications or that can beused with a fiber array. In some cases, optical fibers are twist fusedto form a 2 to 1 “Y” branch, for example, for coupling a pumping laserto a single, signal carrying, fiber. For one-dimensional arrays ofdevices, Y branches have been created on the surface of a wafer bypatterning, using lithographic techniques, to form waveguides. Thistechnique provides robust control for a one-dimensional array, butcannot be extended into two dimensions since it is inherently a planarprocess.

Other methods for making structures for guiding light center around afield known as “photonic integrated circuits” and approaches for makingthem fall into three general classes.

The first class, shown in FIG. 31, involves patterning waveguides 3102on top of a substrate 3104. By way of example, the waveguides 3102 canbe polyimide and the substrate 3104, glass. The problem with thisapproach is that it is not applicable for 2-dimensional array formattingsince the intended height of the waveguides 3102 can be as much as 30microns, but must have sub-micron tolerance and uniformity across thesubstrate 3104. For mass production, this typically means across an 8inch or larger wafer. Obtaining this level of accuracy is prohibitive ifnot impossible to achieve for waveguides 3102 patterned above thesubstrate 3104.

The second class, shown in FIG. 32, involves defining waveguides 3202within a substrate 3204 using an implant or irradiation technique tochange the refractive index of the substrate 3204 in various regions.The problem with this approach is that the typical refractive indexchange between the implanted or irradiated region is a gradient that isso small relative to the substrate that unacceptable levels of lightleakage can occur at bends, turns or tapers in the structure. Thus, thisapproach is poorly suited for waveguides that are not straight.

A hybrid approach, shown in FIG. 33, using a combination of the firstand second class approaches, defines regions 3302 in the substrate 3304by implant or irradiation and uses pattern etches 3306 on top to boundthe light. However, the same loss problems typical of the second classof processes occur. In addition, most substrates that would be used inan etch process, such as in the first and hybrid approaches, are glassesor crystals which are difficult to etch to significant depths, forexample, 30 microns or more, with an accuracy of 1 micron or less.

A third class uses voltage to define waveguides. However, this classsimilarly has problems typical of those occurring with the second classof processes. In addition, this class has the further disadvantage ofrequiring the application of electric power to define the regions, whichis highly undesirable.

In addition, whatever form of waveguide, collimator or coupler is used,if such devices are used in connectors, they must be able to withstandthe stresses of repeated connecting to and disconnecting from a matingpart without incurring damage or detrimentally affecting the accuratefiber alignment necessary for proper operation.

Thus, there remains a need in the art for high accuracy, low losswaveguides or couplers that can be manufactured on a commercialproduction scale and can stand up to repeated connectorization.

SUMMARY OF THE INVENTION

We have created a processing and fabrication technique for multi-pieceferrule technology that satisfies the different needs in the art. Withour approach, a female format high-precision ferrule piece used in afemale side of a device or connector is modified so that alignment pins(also referred to as guide pins) from a male format component, withwhich the female side will mate, do not damage the high precision piece.

By applying the teachings herein, fabrication of optical coupling andwaveguiding elements according to a simple, but highly accurate,processing scheme is made possible. Moreover, these optical coupling andwaveguiding elements exhibit extremely low loss of light through thestructures, particularly where the light path includes bends, turns ortapers.

Advantageously, the technique is scalable, permitting concurrentmanufacturing of multiple such devices on individual wafers,irrespective of wafer diameter, the only limitations being the numberand size of the devices that will fit within a wafer's area and/or thenumber of wafers that can be concurrently etched and/or oxidized. Suchlimitations however, are independent of the invention.

By using our approach, optical coupling and waveguiding elements can bemade at a lower material cost, in a highly accurate manner, on aproduction scale previously unavailable, and in a manner that is notoverly labor intensive.

Moreover, the technique allows the creation of optical elements thatprovide additional benefits because they can be fit into a connector,may or may not hold optical fibers, and can add a third dimension offreedom. This enables the construction of not only fiber holdingelements, but also collimator arrays, Y branch, two-dimensionalwaveguides, and three-dimensional optical integrated circuits.

One aspect of the invention involves a female format connector, usablefor connection with a male format connector having at least onealignment pin. The female format connector has a housing, a ferrule,contained within the housing, comprising at least one high-precisionpiece coupled to a low precision piece. The low precision piece has afirst alignment opening dimensioned to accept the alignment pin of themale format device. Prior to being coupled to the low precision piece,the at least one high-precision piece has multiple fiber holes and asecond alignment opening. The first and second alignment openings aresized and positioned to provide accurate alignment between thehigh-precision piece and the low precision piece during coupling of thehigh-precision piece and the low precision piece to each other. Aftercoupling, the high-precision piece is modified such that the secondalignment opening after modification is larger than the second alignmentopening prior to the coupling.

Another aspect of the invention involves a female format connector,usable for connection with a male format connector having at least onealignment pin. The female format connector has a housing, a ferrule,contained within the housing, comprising at least one high-precisionpiece coupled to a low precision piece. The low precision piece has afirst alignment opening dimensioned to accept the alignment pin of themale format device. Prior to being coupled to the low precision piece,the at least one high-precision piece comprises multiple fiber holes anda wall surface defining a second alignment opening. The first and secondalignment openings are sized and positioned to provide accuratealignment between the high-precision piece and the low precision pieceduring coupling of the high-precision piece and the low precision pieceto each other. After coupling, a portion of the high precision piece isremoved.

A further aspect of the invention involves a method of forming a femaleformat ferrule involves coupling a high precision piece, having a firstwall defining a first alignment hole, to a low precision piece, having asecond alignment hole, the first and second alignment holes being sizedto accept a common alignment pin for maintaining accurate alignmentbetween the high precision piece and the low precision piece during thecoupling, and after the coupling, removing at least some of the firstwall.

These and other aspects described herein, or resulting from the usingteachings contained herein, provide advantages and benefits over theprior art. For example, one or more of the many implementations of theinventions may achieve one or more of the following advantages orprovide the resultant benefits of: longevity through repeatedconnectorizations, ease of insertion into a large format ferrule, highyield, low cost assembly, high precision, design scalability,application scalability, integration into standard commercialconnectors, compatibility with commercial connector through-holepin-placement, manufacturability in a mass-production wafer scaleprocess, compatibility with the thermal coefficient of expansion ofsilicon chips used for transmission and reception of data, lowermaterial cost, lower labor cost, high two- and three-dimensionalaccuracy (since etches can be placed with lithographic precision andoxidation further increases this precision), pieces can be stackedarbitrarily and/or large numbers to make waveguides which change in two-or three dimensions along their length, collimated couplers, opticalrouters, etc . . . , individual wafer thickness is irrelevant, socheaper, less controlled material can be used, stacking on a wafer basisrather than on a piece basis to allow for integration on a massivescale.

Additional advantages achievable in some variants include: the abilityto easily create highly accurate two-dimensional and three-dimensionallight directing structures inexpensively, through the use ofcommercially available silicon wafers, since silicon wafers of exactingthickness are widely available; ease of manufacture, since patterningand etching of silicon can be accomplished to very accurate sizes anddepths; wafer scale manufacturability, because the processes used areall compatible with current wafer scale fabrication techniques; and,creation of very high-confinement optical structures, having smoothsidewalls of a highly uniform, extremely controllable refractive indexmaterial, so that almost all light entering the resultant guidestructure will be transmitted through it.

The advantages and features described herein are a few of the manyadvantages and features available from representative embodiments andare presented only to assist in understanding the invention. It shouldbe understood that they are not to be considered limitations on theinvention as defined by the claims, or limitations on equivalents to theclaims. For instance, some of these advantages are mutuallycontradictory, in that they cannot be simultaneously present in a singleembodiment. Similarly, some advantages are applicable to one aspect ofthe invention, and inapplicable to others. Thus, this summary offeatures and advantages should not be considered dispositive indetermining equivalence. Additional features and advantages of theinvention will become apparent in the following description, from thedrawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded view of a commercial connector assembly;

FIG. 2 shows an example connector hole and fiber;

FIG. 3 shows fibers not centered within holes of FIG. 2;

FIG. 4A shows a one-dimensional fiber array having fibers placed inV-Grooves etched into a piece of silicon;

FIG. 4B shows a stack of two one-dimensional fiber arrays of FIG. 4A;

FIG. 4C shows a hypothetical large format stack of three one-dimensionalfiber arrays of FIG. 4A;

FIG. 5 shows an example of a low-precision piece in accordance with theinvention;

FIG. 6 shows an example of a low-precision piece that is also part highprecision piece;

FIG. 7 shows an example wafer created using one variant of the techniquedescribed herein;

FIG. 8, shows a silicon wafer created using another variant of thetechnique described herein;

FIG. 9 shows a silicon wafer created using another variant of thetechnique described herein having a feature for accurate alignment ofthe wafer relative to another wafer and/or holding of the wafer;

FIG. 10A shows an example high precision piece made using one variant ofthe technique described herein;

FIG. 10B shows an example high precision piece incorporatingmicrolenses, made using another variant of the technique describedherein;

FIG. 11 shows a high-precision piece set up to mount flush on a face ofa low-precision piece;

FIG. 12 shows a tapered piece having a potentially large angle ofinsertion;

FIG. 13 shows one approach to ensuring that an angle of insertion isminimized;

FIG. 14 shows a second approach to ensuring that an angle of insertionis minimized;

FIG. 15 shows a third approach to ensuring that an angle of insertion isminimized;

FIG. 16 shows a variant comprising two high precision pieces and achamber;

FIG. 17 shows another variant comprising two high precision pieces and achamber;

FIG. 18 shows one hole for a high-precision piece superimposed over anoptical fiber;

FIG. 19 shows two fiber holes of the same size as in FIG. 18 ondifferent high precision pieces according to a variant of the invention;

FIG. 20 shows the holes of FIG. 19 holding the optical fiber of FIG. 18where the offset is equally divided between both pieces;

FIG. 21 shows one example of a three piece holder approach;

FIG. 22A shows four wafer pieces or slices with a two dimensional arrayof holes in the center of each slice;

FIG. 22B shows the wafer slices of FIG. 22A in stacking order;

FIG. 22C shows the stack of FIG. 22B being aligned on alignment pins;

FIG. 22D shows the stacked wafer slices of FIG. 22C connected to form ahigh precision waveguide piece;

FIG. 23 shows a series of semiconductor wafer pieces fabricated withholes nearly the same size along with cutaway views of two variantsthereof;

FIG. 24 shows one example tapering waveguide variant;

FIG. 25 shows an example of a two dimensional array of optical Ybranches created using one variant of the techniques described herein;

FIG. 26A shows a more complex, combination application of the techniquesdescribed herein;

FIG. 26B shows a microlens array stacked with two high precision piecesand a low precision piece to create an ferrule compatible with an MTP,MPO, MPX or SMC style connector;

FIG. 26C shows a single optical device focussing light between a deviceand a single mode fiber using the arrangement of FIGS. 26A and 26B;

FIG. 27 is a photograph of a high precision piece created according toone variant of the techniques described herein;

FIG. 28 is a photograph of the piece mounted in a low precision piece asdescribed herein showing the alignment pins;

FIG. 29 is a photograph, in ¾ view of a ferrule for use in an MTPconnector superimposed against a penny;

FIG. 30 is a photograph of a fully assembled MTP connector as describedherein having 72 light carrying fibers;

FIG. 31 shows one class of waveguide;

FIG. 32 shows another class of waveguide;

FIG. 33 shows a hybrid of the classes of waveguides of FIG. 31 and FIG.32;

FIGS. 34A-34C are example variants for avoiding stressing a highprecision piece in a female connector;

FIG. 35 is an alternative example of a variant for avoiding stressing ahigh precision piece in a female connector;

FIG. 36 is an additional alternative example of a variant for avoidingstressing a high precision piece in a female connector;

FIG. 37 is a further alternative example of a variant for avoidingstressing a high precision piece in a female connector;

FIG. 38 is a top and side view of a portion of a wafer where theopenings of holes have been reduced by plating, or treatment with areactive gas;

FIG. 39 is a set of thickness vs. time curves for the oxidation ofsilicon based upon the Deal-Grove equation;

FIG. 40 is an example of the through-hole format light guidingstructures;

FIG. 41 is an example of a waveguide format light guiding structures;

FIG. 42 is an example of a piece combining through-hole and waveguideformats;

FIG. 43 is an example of a more complex geometry light guiding structurecombining through-hole and waveguide formats; and

FIG. 44 is a photograph of a cross section of a guide structure madeusing the through-hole format.

DETAILED DESCRIPTION Overview

In overview, the technique uses one or more high-precision pieces thatcan be combined with a low precision piece to form a ferrule-like unitand then integrated into a commercial connector as the ferrule theconnector is designed to receive.

Low Precision Piece Creation

An example of a low-precision piece 500 is shown in FIG. 5. As shown,this particular shape piece is designed in the shape of a ferruleopening in an industry standard connector apparatus so it can beinserted into a commercial connector, for example, in place of theferrule 102 of FIG. 1. In practice, this currently means the pieceshould typically be shaped to dimensionally fit into at least one of anMTP or MPO or MPX or SMC style connector. Depending upon the particularvariant, the low-precision piece 500 is manufactured by, for example, apolymer molding technique, for example, injection molding, transfermolding, or by some other molding, milling or forming technique. In somevariants, the material used for injection molding is a glass filledepoxy, although other epoxies or plastics can be used. Alternatively, inother variants, the material is either metal or some other moldable ormillable material.

The low-precision piece is manufactured to the outer dimensions to allowit to be properly inserted into the desired connector. In addition, ittypically has an opening 502 that is large enough to receive the highprecision piece(s).

In some variants, the “low precision” piece may also be, in part, a highprecision piece, for example, as shown in FIG. 6, if the low precisionpiece 600 is made out of metal and has a thin face 602 that can beprocessed with holes 604 as described below. However, it is expectedthat such variants will lack many of the advantages of using separatelow- and high precision pieces, but may achieve other advantages orbenefits due to the particular application it is being used for or in.

High Precision Piece(s) Creation

By way of representative example, the technique for creating thehigh-precision piece(s) will now be described using a wafer of siliconas the starting point.

While in some variants, silicon is used as the starting material forforming the high-precision piece(s), in other variants, materials suchas quartz, sapphire, ceramics, glass, other insulators, othersemiconductor wafer compounds, polymers such as polyimide, or metals,such as aluminum or tungsten or alloys, can be used.

The overall manufacturing process for the high-precision piece(s)proceeds as follows:

a) The wafer is processed into a series of chips by etching holesthrough the wafer using either an etching or drilling process. In somevariants, this is done through a semiconductor lithography processcombined with an etching technique. In other variants, laser drilling isused. The holes are each of specific sizes and, where appropriate,axially offset at a specific angle relative to the plane of the wafer(or piece once cleaved). Features such as holes for alignment pins orbumps and recesses for precision mating are also created, whereappropriate. The wafer contains many copies gf the chips that will beneeded to make a particular high precision piece, for example, fiberholding piece, a collimator, many-to-one taper or Y branch. The piecesto build up an element of a particular type can be processed on a singlewafer or by making several wafers, each having some of the pieces neededto make the component. In either case, the resultant wafer scale batchprocessing is the same and saves costs.

The holes are classified into two groups: those which are made for fiberinsertion and/or receiving an optical epoxy, and those that are foralignment and/or placement into a connector. Although in the ideal case,the holes are perfectly cylindrical, frustoconical, obconic or funnelshaped, in practice the holes may only be substantially cylindrical,frustoconical or funnel shaped. However, those deviations, for purposesof the processes described herein, are considered negligible since theyare either a) much smaller than the optical fiber diameter and hencehave no meaningful effect on placement or performance in the case offiber holding embodiments, or (b) virtually irrelevant in the case ofwaveguide embodiments.

In addition, for the variants described herein, to facilitate fiberplacement or create certain waveguide arrangements, in some cases it maybe desirable to intentionally use cylindrical, frustoconical, obconic orfunnel shaped holes that have a substantially oval, substantially eggshaped or substantially elliptical cross section perpendicular to theiraxes (i.e. they are not round). In other variants, different shapedgrooves or grooves in some combination with holes are used.

FIG. 7 shows an example wafer 700 created using one variant of thetechnique described herein. Each piece 702 (also called a slice)contains a central group of small holes 704 (in this case 72 per piece)for fibers and larger holes 706 on the left and right sides of eachpiece for alignment of the piece relative to some other piece.Typically, the number of holes will be equal to or some multiple of thenumber of fibers in a commercial optical fiber bundle, for example,bundles of 6, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132 or 144fibers.

FIG. 8, shows a silicon wafer 800 created using another variant of thetechnique described herein. As shown in FIG. 8, there are small holes802 in each piece 804 within the central area of the wafer for fibers oroptical epoxy and large holes 806 near the edge of the silicon wafer foralignment on a wafer basis.

Additionally, or alternatively, the alignment holes can be part of eachpiece and specifically be spaced so that the piece may be inserted intoan MTP, MPO, MPX, or SMC or other widely available style commercialconnector, such as shown in FIG. 1, as part of or in place of a ferruleand also aligned using alignment pins 110 that are on a part 112 of theconnector itself.

Additionally, other holes or features may be etched into the piece toallow the insertion of epoxies, solder, or some other fastening agent tohold the piece to the low precision piece or so that two or more of thepieces can interlock with each other.

Depending upon the particular variant, in some cases, one or more of thealignment holes on one or more of the components may optionally have anoblong or oval shape to allow some freedom of movement.

Depending upon the particular variant, the particular grooves or holesmay have straight or tapered sidewalls.

In some variants using straight holes, the holes are created by laserdrilling. In other variants, the straight holes are formed using anetching process, for example, anisotropic hole etching. By way ofexample, for a silicon wafer, anisotropic deep/via hole etching ofsilicon is performed by photoresist patterning the wafer according tothe desired hole placement and etching using the Bosch process in ahigh-density plasma reactor such as either an electron cyclotronresonance (ECR) or inductively coupled plasma (ICP) reactor. The Boschprocess is based off of a time multiplexing scheme separating the etch(SF6) and passivation (C4F8 sidewall protection) cycles. The etch causesscalloping on the silicon sidewalls and sharp edges at the base of thevia but the profile produces nice straight holes/vias. Since thescalloping creates edges that are too sharp for fiber insertion withouta guiding structure to help the fiber avoid the edges at the base of thestructure, clean-up etching is required.

Both the clean up etching process and the process of creating taperedholes is essentially the same. In addition to the Bosch process, forclean up and creating tapered holes, an isotropic (non-directional)silicon wet etch (HF:HNO₃, 1:1) is used. This produces smooth, damagefree tapered surfaces. In addition, the isotropic wet etch eliminatesand/or reduces the scalloping and sharp edges created from the Boschprocess, making fiber insertion easier and more reliable.

Alternatively, holes/vias can be made with a combination of etching withKOH and the Bosch process. Both KOH etching and Bosch process etchingare well understood and used widely. Etching of silicon using KOH isalso well known and is used in the micro-machining industry and themicro electro mechanical systems (MEMS) area.

In the alternative variants, a Bosch etch is used on the front side ofthe (100) silicon wafer. Then a SiN_(X) stop layer for the KOH isdeposited in the Bosch etched front side hole. The back side of thewafer in then photoresist patterned in alignment with the front side ofthe silicon wafer. The back side is then wet etched with KOH. TheSiN_(X) is then removed. The scalloping and sharp edges are thensmoothed with HF:HNO₃, (1:1). This process produces a via hole that isboth sloped and anisotropic with a sidewall profile that facilitatesfiber insertion.

The process is similar to create the pieces using other materialsexcept, the specific etch process used will differ based upon theparticular material being used. Since techniques for etching and/ordrilling of holes in other materials such as ceramics, glass, otherinsulators, other semiconductor wafer compounds, polymers such aspolyimide, or metals, such as aluminum or tungsten or alloys are allpresently known and can be applied in a straightforward manner basedupon the teachings contained herein, the specific details of performingsimilar/analogous operations, on the other materials, are omitted forbrevity.

In addition, by optionally orienting the wafer during the etchingprocess and using a dry etching processes, it is possible to etch theholes in a preferred direction or at a specified angle. This isdesirable since a controlled angled insertion allows higher efficiencycoupling into single mode fibers (i.e. non-tapered holes can be etchedat a specified angle, for example, an angle up to about 8 degrees withrespect to a perpendicular to the wafer surface, and thus allow insertedfibers to be accurately held precisely at the specified angle). Thisallows a ferrule for single mode fiber to be easily and inexpensivelycreated.

b) Depending upon the wafer material's refractive index, the waferand/or the holes or grooves can optionally be coated with a thin layerof metal deposited, for example, by such techniques as sputtering,evaporation, electroplating or electroless plating or can be treatedwith a reactive gas to cause the wafer material to create a coating ofreacted wafer material on the exposed surface that reduces the index ofrefraction and/or allows for hole size optimization, for example, in thecase of a silicon wafer, treating with steam at high temperature causesthe surface to oxidize into silicon dioxide. In addition, the oxidationprocess reduces the hole size in a very even, precise and controllablemanner as the material is oxidized over time.

c) Portions of the wafer may also optionally have a dielectric, solderor other adhesive deposited on it, for example, by surrounding some ofthe holes with a ring of reflowable solder a few microns thick or usingdeposition techniques such as sputter deposition.

d) In some variants, the wafer is then diced into individual pieces. Inother variants, for example, in a batch manufacturing process, the wafermay not be diced until after any of e), f), g), h) or i) below dependingupon the particular wafer, type of arrangement being created or othermanufacturing reasons irrelevant to understanding the invention.

e) The wafers or individual wafer pieces are stacked onto alignmentpins.

Depending upon the particular application differing methods will be usedfor alignment, for example, holes 802 can be placed for alignment on awafer basis (as shown in FIG. 8), rather than on an individual piecebasis. Alternatively, instead of using alignment pins, on a wafer ofpiece basis, a wafer 900 can have some other feature, for example, anotch 902 and/or flattened portion 904 such as shown in FIG. 9 foraccurate alignment and/or holding of the wafer. In some variants, othertechniques for alignment can be used, such as, putting the pieces into aholding jig or using interlocking complementary features etched intoeach piece.

f) The wafers or individual wafer pieces are then fused together, forexample, by heating and melting the solder, which fuses the piecestogether, or by using other bonding techniques including, those usingpressure, adhesives or mechanical devices such as clips, screws orrivets.

g) Optionally, if the holes will not directly hold fibers or hold anelement like a microlens or diffraction grating, optical epoxy and/ordielectric material(s) are flowed and/or sputtered into the holes and,in the case of epoxy, cured to harden it.

h) The alignment pins are optionally removed, and

i) The end faces of the piece are polished to optical quality.

The final piece can also be ground down, prior to, or after, step i), toany specific final shape desired, since the shape of the high-precisionpiece as it goes into the low precision piece can be different from theshape after the pins are removed or the pieces are diced.

It should be noted that the above steps need not be performed inprecisely the order specified. Since the various permutations andcombinations are to numerous to detail, it should be understood that, insome cases, the order can be changed without changing the invention.

Some example variants use a wafer-at-a-time process for creating thehigh-precision pieces in bulk. By making the pieces in wafer form, largenumbers of pieces can be made simultaneously, thus keeping the costsdown. As shown in FIG. 7 over 220 pieces can be made on a single waferat one time. Typically, if an industry standard four inch wafer is used,over 400 pieces for an MTP connector ferrule can be made per wafer.Using an eight inch wafer, allows production of three to four times thatnumber.

Connector Creation

The connector is created by combining the high precision piece(s), thelow-precision pieces, inserting the fibers, and incorporating thecombined piece into the remainder of the connector.

The high precision piece(s) are inserted into a recess in thelow-precision piece and secured, for example, by being epoxied intoplace to hold the pieces together. FIG. 10A shows an example highprecision piece 1000 made of silicon using one variant of the technique.As shown in FIG. 10A, the corners of each high precision silicon pieceare chamfered 1002, specifically at 45 degrees, to allow a region ofspace, between the high precision silicon piece 1000 and the innermostedge of the receiving portion of the low precision piece, for afastening agent. As noted above, other features or holes can be usedalong with or instead of the chamfers for a similar purpose.Alternatively, as shown in FIG. 11 the high-precision piece 1102 can beset up to mount flush on a face 1104 of the low-precision piece 1106.

It is also important to place the high precision piece accurately on orinto the low-precision piece so that the fibers in the connector willalign properly with their counterparts. This can be done, for example,by inserting an alignment piece 106 (such as shown in FIG. 1) containingalignment pins 110 which will protrude through holes 1108 in thelow-precision piece and then through the alignment holes 1110 in thehigh precision silicon piece 1102.

Depending upon the particular connector, the alignment pins can beremoved at this point and not used in any further operation, if they arenot needed or not desired for the particular use (thereby creating afemale version) or they can remain in (to thereby create a maleversion), for example, as would be the case for the MTP connector ofFIG. 1.

As noted above, both the high precision piece and the low-precisionpiece have alignment pin holes which allow the accurate insertion of thehigh precision piece into the low-precision piece. The high-precisionpiece is inserted by placing alignment pins through the holes in boththe high-precision piece and the low-precision piece and then slidingthe two pieces together. Because the alignment pins as well as theplacement and size of the holes in both pieces is very accurate, the twopieces are aligned to a very tight tolerance.

In the male version of the connector the alignment pins are permanentlyinserted into the connector. In the female version of the connector, thepins are removed. When a male and female connector are joined, if theconnector contains a female side high precision piece, the alignmentpins in the male side of the connector slot through the high-precisionpiece holes into the holes in the female side low-precision piece. Thehigh precision piece is thin and strong but brittle, so that, for thefemale piece, repeated alignment pin insertion results in increasedstress during connector combining that can ultimately cause the highprecision piece to crack.

Since the holes in the low-precision piece alone can supply the requiredaccuracy in mating male and female pieces, and provide the necessarystrength in connection, the alignment pin holes in the high-precisionpiece are not essential for proper operation. Their primary function isfor accurately placing the high-precision piece into the low-precisionpiece. Once the high precision piece has been affixed to thelow-precision piece, the need for the alignment pin holes in the highprecision piece is eliminated. Thus, to avoid creating a crackingproblem, the general procedure described above is slightly different forcreating a female side connector than for creating a male sideconnector. In overview, the procedure is as follows:

A low-precision piece in which the spacing accuracy of the alignment pinholes, and the depth into which the alignment pins will insert intothose holes, is sufficient to align and hold a connector together evenif no high precision piece were presents is created.

A high precision pieces with accurate alignment pin holes is alsocreated.

The alignment pin holes in each are used to properly place thehigh-precision piece relative to the low-precision piece.

Thus, in greater detail, for both male and female pieces, the assemblyprocess is initially the same. The high precision piece, containingholes for fiber placement and holes for alignment pins, and thelow-precision piece, containing a location to situate the high precisionpiece and alignment pin holes, are brought together.

Alignment pins are then inserted through the low-precision piece so thatthey extend a sufficient distance beyond where the high precision piecewill be attached.

The high precision piece is then inserted onto the alignment pins andseated against the low-precision piece. At this point, the highprecision piece is positioned extremely accurately with respect to thelow-precision piece.

The high precision piece is then fixed in place, for example, using anepoxy, to create the complete ferrule.

For a male side connector, the alignment pins are left in-place. For afemale side connector, the alignment pins are removed.

Female side pieces are then further processed by modifying the alignmentpin holes of the ferrule so the high precision piece is not overstressedby repeated attaching and detaching of a connector. Thus, for a femalepiece only, the alignment pin holes, in only the high precision piece,are either:

a) ground or etched larger, either for their entire diameter, in afunnel (i.e. tapered or cone) shape, oblong shape, or other shape thatsufficiently enlarges the alignment pin hole 3402 in the high precisionpiece 3404 (shown in front view and with exaggerated thickness in sideview in FIGS. 34A-C) relative to the size of an alignment pin 3406);

b) partially removed (FIG. 35); or

c) fully removed (FIG. 36),

so that the alignment pins from a male connector can easily pass throughor by the high precision piece without stressing it. The alignment pinholes on the low-precision piece are, however, kept to an original tighttolerance so that the two pieces can be accurately connected in arepeatable manner. In practice, using a funnel shape for the holes, forexample by polishing, ensures that the entrance to the high precisionpiece is wider than the alignment pin to avoid excessively stressing thepiece and also allows the hole to direct the alignment pin towardsproper placement.

In alternative variants, hole modification may be partly performedbefore the high and low-precision pieces are joined. This can occur in afew different ways. If a funnel shape is used, the hole size near onesurface or the other surface of the high precision piece must beunchanged. If the holes will be partially or completely removed prior tojoining (FIG. 35), as in FIG. 35 or 36, one or both sides can be partlyremoved, so long as enough of the two alignment holes remains (to acceptthe guide pins in the proper spacing) before joining. If the holes willultimately be completely removed, one end of the piece can be removed,provided the edge surface 3702 at a perpendicular to the plane 3704through the centers 3706 of the alignment pin holes maintains the properspacing (FIG. 37).

If a funnel type or partial-hole removal modification is done, anoptional strengthening coating can be applied to the surface of the coneshape or wall of the part of the hole that remains to harden the surfaceand prevent or reduce scratching. Depending upon the particular case,this coating can be a metal, such as gold, or a harder substance such assilicon nitride, silicon carbide, diamond thin films, etc. which can bedeposited as required on a piece, multiple piece, or wafer at a time,basis.

Fibers are inserted through the low-precision piece and then through thehigh precision piece so as to terminate in, or just beyond the outerface of the high precision piece. The low-precision piece then is filledwith epoxy to hold the fibers in place via, for example, an inlet formedin the piece. If desired, the combined unit can then be polished so thatthe ends of the fibers are flush with the face (i.e. the front) of thecombined piece or slightly protruding. Optionally, the face of the piecewhere the fibers are visible can be coated with a diamond thin film (orother hard material) to prevent the silicon from being worn down duringthe polishing process.

Feature Optimization

In order to have accurate fiber placement, the wafers that are used aretypically relatively thick, for example, at least the thickness of anoptical fiber or about 100 microns. However, holes that will receiveoptical fibers must be accurate, in diameter or in their narrowestdimension in the case of non-round or oval holes, to approximately 1micron. In some variants however, this tolerance is extremely tight andcan be difficult to consistently achieve from wafer run to wafer runand/or to maintain with consistency across entire wafers, whichpresently range from 4 to 12 inches in diameter, for silicon wafers.

Advantageously, we can form an array of features, such as grooves,holes, bumps or posts in a wafer of material in such a way that, afterthe forming is performed, the wafer can be post-processed to optimizethe size of the features to extremely high accuracy, for example, lessthan ±1 micron. In fact, this technique is applicable to any analogouscircumstance where great accuracy in sizing is required.

Referring to FIG. 38, the process will now be described with referenceto partial top and side views of a portion of a single high precisionpiece 3800 that has multiple through holes 3802, 3804 that will eachcarry a single optical fiber. While FIG. 38 shows the process withreference to a portion of a single high precision piece 3800, it shouldbe understood that the process will typically be performed on a wafercontaining hundreds or thousands of pieces. For simplicity, only twoholes 3802, 3804 on the single piece 3800 are shown. In addition, itshould be understood that the piece may also have other non-fiberbearing features, such as waveguide features, indentations, bumps, etc.and, should there be a need to post-process any of them for highaccuracy, the process will be the same for them.

In practice, for an optical fiber specified at 125 microns in diameter,it is desirable that the hole in the piece that will hold the fibertypically be between about 125.5 microns and, preferably, about 127.5microns in diameter on the end that will be closest to the device (e.g.lasers and detectors) that will be coupled to the fibers (referred to asthe “activity end”). However, due to imprecision in processingtolerances, fiber hole diameters can vary from wafer to wafer or acrossa wafer such that, despite process controls, they can be as much as 130microns in diameter. Since this small (2.5 micron) difference can beconsidered substantial, relative to the placement accuracy typicallyrequired, the difference can be corrected in the following manner.

First, the activity end of the fiber holes are measured to determinetheir deviation “D” from the desired diameter.

Next, a metal, for example gold, is deposited on the wafer 3800including the walls of the holes 3802, 3804, for example by sputterdeposition, to provide a thin conductivity layer 3806 over the exposedmaterial. Depending upon the particular variant, this can be done oneither one or both sides of the wafer. If metal is sputtered only on oneside, then the holes will typically have covering only about half wayinto the depth of the holes. This creates, in effect, a partiallytapered hole. Moreover, sputtering the metal on one side is typicallysufficient, since the accuracy of hole diameter is most important on theactivity end when the feature is a hole for fiber placement.Alternatively, if the wafer is made of a conductive material or at leasta highly doped semiconductor material, then depositing of the metal maybe omitted, unless electroless plating is used.

Depending upon the particular case, the wafer is then eitherelectroplated or is put through an electroless plating process in orderto build up a material layer 3808 on the conductive surfaces. Dependingupon the particular case, the plating material can be gold, silver,zinc, or other materials can be used. The electroplate/electrolessplating process builds up the material on the conductive surfaces in aneven fashion (i.e. the thickness grows on the hole walls at about thesame rate as it grows on the flat surface of the wafer). Moreover, thegrowth rate can be precisely controlled so that the holes are filled,from the sides inward, until the diameter of the hole “d” at the exit isthe desired thickness.

Thereafter, the processing occurs according to one of the variantsdescribed herein.

In some variants, wafers are polished prior to plating so that nomaterial is plated on the surface, but it is the holes. In yet othervariants, wafers are polished after plating to remove the platingmaterial from the surface. In other variants, the post-plated wafer canbe partially polished, so that some plating material remains so thatremaining metal can be used in a metal-to-metal fusion process to jointhe wafer to another (or one or more of its pieces to others). In stillother variants, some of the deposited metal is selectively removed fromparticular features or surfaces by further processes to further controlthe location(s) where the plating will occur.

Alternatively, hole size can be controlled in an analogous fashion, forsome materials, through treatment of the wafer with a reactive gas. Forexample, as described in greater detail below, by exposing a siliconwafer to steam under the right conditions, for example as determinedusing the Deal-Grove equation, the silicon will oxidize into silicondioxide. While this oxidation process changes the index of refraction ofthe silicon, because silicon oxides are not as dense as the siliconwafer itself, the reaction also causes the surface to grow. As a result,oxidation of a hole will cause the wall of the hole to grow inward andreduce its overall diameter. Since these treatment processes can also behighly controlled, in some variants they can be used instead of theplating process. In some variants, both processes can also be used, fordifferent features in the same area of the wafer or for different areas.

Applications

The processes described above for creating the different pieces havenumerous applications. A few will now be described in simplifiedfashion, bearing in mind that more complex arrangements and/orcombinations of the described applications can be readily created usingvariations on the techniques and applications described herein.

Ease of Insertion Variants

Pieces, which have a wide opening on the side where fibers will beinserted while having a narrower opening at the point where the fibersexit, can be used to make fiber insertion easier.

As shown in FIG. 12, a tapered piece 1200 by itself would result in apotentially large angle of insertion “θ” because the fiber will not beconstrained within the piece in a particular position owing to the factthat it can be inserted at an angle, rather than straight in. This isnot desirable since it can cause a loss of light when coupling lightbetween two such connectors or when connecting a fiber bundle to acomponent that emits, detects or routes light.

In order to ensure that the angle is minimized, any of four basicapproaches (or some combination thereof) are used.

Approach 1: Two high-precision pieces 1300, 1302, having taperedsidewalls 1304, 1306 are stacked on top of one another so a fiber 1308has to pass through two narrowing regions (the tapered sidewall holes)which are separated by a space (of typically either the thickness of thelast piece to be passed through or that thickness plus some otherdistance). This is illustratively shown in FIG. 13. Ideally, in such acase, the hole on the side of the piece into which a fiber will first beinserted will have a diameter W and the hole on the opposite side willhave a diameter X, where W>X. Ideally, the diameter X will be close tothe diameter of the fiber, although it will likely be larger. The otherpiece will have a hole, on the fiber entry side, of a diameter Y whichcan be any size equal to, or between, W and X. The exit side of theother piece will have a hole diameter of Z, where Y≧Z.

Approach 2: The two high-precision pieces 1400, 1402 are stacked on topof one another as above, but the first one to be entered by the fiberhas tapered sidewalls 1404 and the other is etched or drilled with“straight” sidewalls 1406 (i.e. they may, or may not, be angled withrespect to a perpendicular to the surface of the piece). The taperedregion allows ease of insertion of a fiber 1408 while the straightregion maintains a low angle of insertion for a fiber 1408. A longerregion of straight sidewalls provides more support and stability for thefiber and thus holds it in place more firmly and without the risk ofedge pieces nicking the fiber. This is shown in FIG. 15.

Approach 3: A single high-precision piece 1500 is fabricated in atwo-step process where the piece is etched in a tapered fashion on oneside 1502 and then etched anisotropically on the other side 1504 so thatthe hole on one side of the piece is tapered 1506 while the other sideof the hole in the piece has straight sidewalls 1508. This results in asingle piece (which saves material costs and assembly time) that allowsfor easy fiber insertion and a low angle of insertion of a predeterminedoffset from a perpendicular to the piece for single mode fibers. This isshown in FIG. 5.

The piece in this approach could be twice as thick as in approaches 1 or2, so as to fit into the same low precision piece. Alternatively, a lowprecision piece specifically designed to accept the piece made usingapproach 3 can be used.

Approach 4: Either two piece approach above is used, but the fiber holesin one or both of the two pieces are made slightly oval, although notnecessarily in alignment with each other. This allows for more flexiblespacing of the guide pin holes to account for inaccuracies in either theguide pins themselves or the guide pin holes, which are sometimes lessaccurate than the fiber holes due to their size.

In still other variants, such as shown in FIGS. 16 and 17, two highprecision pieces 1602, 1604, 1702, 1704 are created as described herein.In addition, a low precision “chamber” 1606, 1706 is also createdbetween the two pieces which can fully surround the fibers (such asshown in FIG. 16), partly surround the fibers (such as shown in FIG.17), or not surround the fibers at all (for example by using precisionstandoffs or spacing posts). In other words, instead of being stackedagainst each other, the high precision pieces 1602, 1604, 1702, 1704will each be separated from each other by the chamber 1606, 1706 or thestandoffs/posts. Individual fibers or a fused tapered one or twodimensional arrayed waveguide structure, either in Y-Branch 1708 orstraight form, is inserted through each of the high precision pieces1602, 1604, 1702, 1704 to create a collimating element, “shuffle”signals passing through the element from one side to the other, orperform a 2 (or more) to 1 mapping of optical devices to optical fibers.Once the fibers are inserted, the high precision pieces 1602, 1604,1702, 1704 are attached to the chamber 1606, 1706 and the chamber orarea around the fibers is filled with an epoxy or other hardening agent.The portions of the fibers extending outside the element are then cutoff, and the exposed faces are polished as noted above. This will allow,for example, a one or two dimensional array of lasers to be coupled ingroups into a separate array of fibers, multiple devices which emit atdifferent wavelengths to be coupled into individual fibers, or multiplelasers at a single wavelength to be coupled into single fibers to allowredundancy during data transmission.

High Accuracy Holding Variants

Two pieces that are designed with commonly aligned fiber holes butalignment holes or other structures that are offset, relative to eachother, can be used to provide greater accuracy in fiber holding thaneither piece can provide alone.

Instead of having the aligning structures in the two pieces in exactlythe same position with respect to the fiber holes, the relationshipbetween the aligning structures and the fiber holes is offset so thatthe fiber holes in the two pieces do not completely line up. FIG. 18shows one hole 1800 for a high-precision piece superimposed over anoptical fiber 1802. Note that the hole is almost 25% larger than thediameter of the fiber. FIG. 19 shows two fiber holes 1900, 1902 of thesame size as in FIG. 18 on different high precision pieces according tothis variant. Instead of the fiber holes being aligned when the piecesare aligned, these fiber holes are offset relative to each other whenthe alignment structures or holes are aligned. The offset isintentionally set at about a predetermined amount, such that the twoclosest parts of the holes are spaced apart by about a fiber diameter.The offset Δ (as shown in FIG. 19), allows two holes which are largerthan a fiber to hold that fiber very accurately since the width of thebiconvex opening 1904 formed by the two pieces, taken along a linepassing through the centers of the holes, is very close to the diameterof the fiber to be placed inside and be closely constrained. Ideally, asshown in FIG. 20, the holes 2000, 2002 are the same size (so the offsetis equally divided between both pieces) so that a single wafer can beused to create one format piece and two identical pieces can be used tohold a fiber 2004 by placing them back-to-back. By way of example, iffor a particular application the fiber holes were, 4 microns too large,offsetting the two pieces by a few microns increases the pitch accuracyfrom a worst-case of 4 microns to as much as a sub-micron accuracy. Thispotentially provides a substantial improvement in coupling efficienciesbetween fibers.

As noted above, elements can be created that combine a high precisionpiece and a low precision piece. Advantageously, if it is possible inthe particular case to make a “low precision” piece with a hole size ofa specified (im)precision but precise offset, then only onehigh-precision silicon piece need be used to hold a fiber with highaccuracy. This further reduces the number of element components fromthree to two. FIG. 11 shows one example of the two piece holder approachand FIG. 21 shows one example of the three piece holder approach usingthe high precision pieces 2100, 2102 having the specified offset Δ and alow precision piece 2104.

The combined pieces can be made in a size and shape that is compatiblewith conventional connectors, for example, the low-precision piece isthe size and outer shape of the conventional ferrule for the connectorof FIG. 1.

Thus, the precision of the fiber hole pitch of the combined unit ishigher than the precision that would be obtained by using orconveniently or cheaply obtainable with any of the individual piecesthemselves.

Waveguide, Coupler and Collimator Variants

The high precision pieces need not necessarily be designed to hold afiber. Instead, an arbitrary number of pieces can be created such that,an individual piece, or a number of pieces once the pieces are stackedcreate a waveguide, coupler or collimating element through etching andfilling the etches with an optically transmissive medium.

Such elements are constructed by patterning structures such as holes orpaths on individual high precision pieces in an aligned or offsetlayered fashion and then stacking those pieces together to form opticalrouting topologies in two or three dimensions. This makes creation ofnot only simple waveguide structures possible, but more complicatedwaveguide topologies, structures to route optical signals through theuse of photonic bandgap engineering materials containing periodicstructure features throughout the material in each of the pieces, orintegration of other elements, for example, (by etching or depositinglenses or diffraction gratings in one or more of the pieces. Throughcreative use of the technique, even more complex geometric arrangementsor combinations can be achieved.

In overview, the waveguides, couplers or collimators are made using thefollowing general process:

Guide structures are formed in the material that forms the frame ofwaveguide, coupler or collimator. The material is then treated with areactive gas to create a low refractive index cladding layer on thesurface of the structures. The remaining volume of the post-treatmentstructure is then filled with a sufficiently high refractive indexmaterial, relative to the cladding layer.

Specifically, in the case of the silicon wafers described herein, theapproach is a s follows.

First, the appropriate guiding structures (cavities) are pattern etchedin the wafer, typically a silicon wafer. Then the wafer is treated witha reactive gas, in the case of silicon, to for example, oxidize theexposed surface, which creates a relatively low refractive indexcladding layer on the surface of the cavities. Alternatively, differentreactive gasses can be used that will turn the silicon into anoxy-nitride or a nitride. Then the remaining cavity is filled with ahigh refractive index material, for example, epoxy. Further optionalprocessing can then be performed such as etching any excess epoxy,polishing, cleaving and/or stacking as necessary.

With our approach to making waveguide, coupler or collimator structuresseveral beneficial aspects are achieved. We achieve precision spacing intwo dimensions for a 2-dimensional array or in two- or three-dimensionsfor a 3-dimensional array, our structures are batch manufacturable sothey are east to fabricate, they can be integrated into commerciallyavailable ferrules and/or connectors, and they have a high confinementfactor (i.e. there is little loss due to the structure itself even ifthe structure has bends, turns, tapers or y-branches in it.), to name afew.

In some variants, the walls of the holes or guides are also coated witha metal layer before the epoxy is flowed into the holes or guides. Inother variants, instead of, or in addition to, the metal layer, a thin,low dielectric material layer is added on top of the metal, prior toflowing the epoxy. In still other variants, the walls of the holes orguides are treated with a reactive gas to, in the case of a siliconwafer, oxidize the silicon into silicon dioxide.

Although, as noted above, silicon wafers can be used to form the guidingstructures, silicon, by itself, generally causes unacceptable losses atshorter optical wavelengths, for example, wavelengths below 1 micron,because it has a very high refractive index (refractive index≧3) andlight tends to migrate to high refractive index materials. This makessilicon less suitable, by itself, for use in creating efficient guidestructures. Thus, for light to be efficiently guided through the holesor along the waveguides, an optically transparent material, having ahigher refractive index than the silicon by itself, must be used to fillthe holes and such materials are not readily available at present.Alternatively, the portion of the silicon that is to guide the lightmust be coated with a material having a much lower refractive index.

Advantageously, in alternative variants, we accomplish this by coatingthe walls of the guiding structure with a low loss relatively lowrefractive index material and then filling the center of each guidingstructure with a low loss, material having a sufficiently higherrefractive index relative to the coating to direct light along theguiding structure. Since both the coating material and filling materialcause low losses and have sufficiently different refractive indexvalues, an efficient guiding structure (i.e. coupler, collimator orwaveguide) is created.

Note that, as detailed above, the epoxy or other material which isflowed into the holes needs to be a higher refractive index than thematerial which is used to form the walls of the holes. If this is notthe case, then the walls of the holes in the wafer pieces that willserve as part of the waveguides are metalized using, for example,electroplating or electroless plating. By “metalizing” the structure wemean that a metal is used to coat the surface of the holes.

Metals however, can also cause unacceptable losses. For example, gold,which has about a 95% reflectivity, can be used. However, duringtraversal of gold coated holes in a structure, light can bounce off ofthe gold 10 times or more. If this occurs, only about 60% of theentering light will exit the structure. Losses of this magnitude aretypically unacceptable in most applications. It is much more desirableto have structures with a greater optical throughput, preferably about98% or better.

Because the coating needs to be of low refractive index, very thin, andvery uniform throughout the guiding structure to be most efficient, atechnique such as sputtering a dielectric with these attributes onto thewalls of the structure can also or alternatively be performed. However,doing so requires extremely good process tolerance in addition to addingfurther steps to the fabrication process.

In cases where sputtering of a dielectric is undesirable, for example,due to the inability to maintain the necessary process tolerances or theincreased costs associated with adding those additional steps, a furtheralternative method may be used.

In this alternative method, the structure is treated with a reactive gasso, in the case of silicon, it is oxidized (the conceptual equivalent ofcausing iron to rust) to form a thin coating of silicon dioxide on thesurfaces of the structure or converted to silicon oxy-nitride or siliconnitride using an analogous process. Since, in this variant, the coatingor cladding is not deposited or made by etching—it is a thermally grownmaterial—it actually smooths out any existing sidewall roughness as itis formed. As a result, it creates a highly uniform, extremelycontrollable refractive index material that can be deposited in a singleoperation to extremely tight tolerance, even over 12 inch siliconwafers.

This coating also causes extremely low loss at optical wavelengths inthe 300 nm to 2000 nm range. Moreover, the refractive index of the oxideof the silicon is approximately 1.46, which is relatively low relativeto that of the silicon itself. Thus, this coating makes it possible tomake a very efficient waveguiding structure by filling the remainingcavity with a high-refractive-index material, for example, an epoxy suchas polyimide which has a refractive index of up to about 1.8. Therefractive index (“RI”) difference between the formed oxide (RI≈1.46)and the polyimide (RI≈1.8) is sufficient to efficiently pass light, eventhrough a long structure and/or from laser sources which are highlymulti-mode, or instances where the light is extremely divergent becauseit exits the laser source at a large angle.

Oxidation of the silicon wafer is performed in a steam environment. Ascan be seen from the Deal-Grove equation based graph of FIG. 39, at atemperature of 1100 degrees Celsius, for example, the silicon wafer willbe oxidized to form a cladding layer of silicon dioxide two micronsthick in about 8 hours. Advantageously, an entire wafer full of guidingstructures can be reacted simultaneously. Thus, even though in theexample, the process takes about 8 hours, hundreds or thousands of partscan be done at one time, so the per-piece throughput is very high.

We have determined that, using this process, on silicon wafers, producesan oxidation layer of silicon dioxide that is extremely uniform. Infact, we have made structures in silicon containing several millimeterlong holes, 50 microns in diameter, and, using the above referencedoxidation process, obtained a silicon dioxide coating on the walls ofthe holes that is uniform to any of our measurable tolerances.

We have further determined that, for a silicon wafer, oxidizing thesilicon until the guide structures have a coating of between about 1 andabout 10 microns is effective, with about 1.5 to about 2 microns ofsilicon dioxide creating a sufficiently thick cladding layer forcommercial practice.

If a material, other than silicon, that has a high refractive index isused, an analogous approach can be employed to similar effect. Guidestructures are formed in the material. The material is then treated witha reactive gas to create a low refractive index cladding layer on thesurface of the structures. The remaining volume of the post-treatmentstructure is then filled with a sufficiently high refractive indexmaterial, relative to the cladding layer, to create the efficient guidestructure.

Our approach uses one of two generic formats. The first format is athrough-hole format, the seconds is a waveguide format. However, becausea wafer scale, batch manufacturing process is used, either or bothapproaches can be used on a single wafer or even a single slab or piece.

Having described this reaction treatment or “oxidation”-type process,the two formats that we have devised will now be discussed withreference to FIGS. 40 and 41.

The first of the two, the through-hole format of FIG. 40D, involvestaking a wafer (FIG. 40A), for example, a silicon wafer, and makingholes in it (FIG. 40B), for example, straight, angled tapered, oval,etc. holes made by etching, drilling, micromilling, etc. the wafer sothat the holes go through the piece, for example, in a one- or twodimensional array.

As noted herein, very precise spacing of holes can be made by etchingsince the patterning can be done via high-precision lithographytechniques and because high-precision, fine feature etching of siliconis a well developed and understood technique. As a result, the siliconetching is described herein, for purposes of illustration, becauseetching silicon is easier than etching other alternative materials, suchas glasses, for example, borosilicate glasses, or dielectric crystals,for example, Lithium Niobate.

Once the holes have been made, in this case etched, the etched holes areturned into guiding structures by treating the wafer with a reactive gasto change the holes into a lower refractive index material to act ascladding (FIG. 40C), for example, for silicon by treating with steam ata high temperature in this case by oxidizing the silicon wafer to createthe cladding layer of silicon dioxide (SiO₂), followed at some point byfilling the holes with a material with a higher refractive index thanthe cladding, e.g. in the example case polyimide or an optical epoxy(FIG. 40D).

In the waveguide format, several layers of wafers will almost always bestacked to make, for example, a two dimensional array. However, unlikewith the through-hole format, the guide structures run along the surfaceof the wafer, such as shown in FIG. 41. This requires extremely precisespacing of wafers in the vertical dimension (FIG. 41A), particularlywhere, at the input or output side of the guide device, a precise pitchmust be maintained. Advantageously, since silicon wafers of precisestandard thicknesses, for example 250 microns. are readily available andhave extremely tight tolerances on both the overall thickness andthickness uniformity, this thickness can be used to accurately space thewafers in the vertical dimension while the precision lithographytechniques maintain accuracy in the horizontal dimension. In otherwords, in contrast to prior art techniques that pattern waveguides onthe silicon wafer, waveguide structures, like trenches or grooves, aremade into the surface of the wafer, for example by etching ormicromilling (FIG. 41B), so that wafers (or pieces thereof) can bestacked top to bottom with consistent wafer tolerance level accuracy.

To make the waveguide format, trench structures are made into thesurface of the wafer (FIG. 41B) and then the wafer is treated with areactive gas to create a lower refractive index cladding on the surfaceof the material and thereby form a cladding layer on that surface (FIG.41C), in the case of silicon it is oxidized into silicon dioxide.Optionally, cladding on the upper surface can be polished off (FIG.41C). A core material coat that has a higher refractive index than thecladding is added, for example, a high-index material, like polyimide,is then put into the formed structures (FIG. 41D) and then any excesshigh-index material that may extend above or be on the top of the waferis removed, for example by etching, polishing or other process (FIG.41E). Optionally, if a metal-to-metal fusion process is to be used, avery thin metal layer is deposited on at least the back of the wafer(FIG. 41F). An appropriate number of wafers 4150 and, if necessary, asuitably treated or oxidized “cap” layer 4152 are then stacked andbonded together (FIG. 41G) by (for example) a wafer fusion process.

Depending upon the particular application to connect multiple pieces ofeither format (or pieces having both formats) direct silicon-to-siliconwafer fusion can be performed.

Alternatively, a metal can be applied to coat mating surfaces of thewafers (FIG. 41F) to make a metal-to-metal wafer fusion possible. In themetal-to-metal case, a thin (preferably much less than a half-micronthickness) layer of metal is used, so that, in the case of the secondformat, the thickness in the vertical dimension is within acceptabletolerances.

In either format, the resultant waveguides, couplers or collimators (ortheir components) can be straight, curved, tapered, have more complexgeometries, or more complex structures and the two formats can be usedon a common wafer or piece as shown in FIG. 42 or FIG. 43.

In the case where multiple through-hole pieces are to be stacked andbonded, the epoxy can be inserted prior to bonding or post-bonding,depending upon the particular circumstances.

In the case where the waveguide format is used, the epoxy will mostoften be inserted prior to bonding.

In the case where a stack will contain both formats, the epoxy willtypically be inserted prior to stacking however, particularconfigurations or geometries may necessitate a combination of pre- andpost-stacking filling or filling only after stacking has occurred.

While the above description was in the context of one piece at a time,in both cases the process is a wafer-scale process. In the through-holeformat, a wafer full of pieces is processed, oxidized and (whereappropriate, epoxy filled) at one time. In the case of the waveguideformat, the waveguide layer created in the wafer surface is done a waferat a time.

In this manner, the resultant wafer can then be diced to produce theindividual pieces that are used as is or stacked, or entire wafers canbe stacked together and the sawn into individual partial or completeunits. Thus, many thousands of devices can simultaneously be producedthereby keeping per-device costs down.

Pieces have been made both in the through-hole and waveguideconfigurations. FIG. 44 is a photograph of a cross section taken of aguide structure made in silicon using the through-hole format. The holeis about 127 microns in diameter and an extremely uniform thin (˜1micron thick) ring of oxidation (silicon dioxide) can be seen on thesurface of the hole.

In addition, through simulations of optical power through differentstructures according to the invention, including a taper and a bentguiding structure, we determined that the high refractive indexdifference between the silicon dioxide and the polyimide (1.46 to 1.8)allows input angles of up to 70 degrees with virtually no loss withinthe structures. This compares very favorably with, for example,traditional optical fiber that allows input angles of up to about 15degrees.

Having described aspects of the process for making waveguides, couplersand/or collimators, some representative specific examples of uses of theabove will now be described.

FIG. 22A shows four wafer pieces 2200, 2202, 2204, 2206 with a twodimensional array of holes 2208, 2210, 2212, 2214 in the center of eachpiece. Note that the holes in each of the arrays of a piece are the samesize, but the different pieces have different size holes with respect toone another. These pieces are then stacked (FIG. 22B) and aligned onrods or pins 2216 (FIG. 22C) so that, when fully integrated, they arepushed together in close contact (FIG. 22D). Once the pieces arestacked, and aligned with respect to one another, the holes are turnedinto an optical guiding medium. This is accomplished by processing thewafers and flowing an optically transparent epoxy into the holes andcuring it into a hardened form. This effectively creates optical fibersinside each of the holes.

FIG. 23 shows a series of semiconductor wafer pieces fabricated 2300,2302, 2304, 2306 with any array of guiding holes, all nearly the samesize. These pieces are stacked on top of one another so that the guidingholes are all aligned. An optical epoxy is flowed through the holes inthe pieces and cured to form the guiding material. Each resultantwaveguide guides light from one end to the other end. As can be seenfrom FIG. 23, a number of pieces can be stacked together to form acollimating element made up of waveguides of arbitrary but controllablelength. For example, if the wafer were 250 microns thick and twelve ofthem are stacked together, a piece 3 millimeters thick would result.

Ideally, if accuracy of alignment can be made high enough, all of theholes should be made perfectly straight to enable a ultra-low-losstransfer of light from one side to the other. However, as will typicallybe the case, if alignment between individual pieces cannot be held totight enough tolerances, each of the pieces can have a tapered hole. Thepieces are then stacked with the smaller end of one piece feeding intothe larger end of the next piece in the direction of expected lighttravel. Thus, if the two pieces are slightly misaligned, the small endwill still allow light to transfer into the next piece through the nextpiece's larger end. In this configuration, it is important that thepieces be arranged so that light will always traverse in the directionfrom the larger ends to the smaller ends to ensure that the maximumamount of light traverses each interface.

FIG. 23 also shows in cross section what one of a series of holes in anarray of holes would look like in a straight sidewalls variant 2308 anda tapered sidewalls variant 2310 after stacking a number of waferpieces. As can be seen, in the example cross sections, thirteen pieceshave been stacked to achieve the resultant shape.

In another variant, by using tapered holes that are intentionallyslightly offset from piece to piece in a particular direction, the holecan direct the light to another location. By using this techniquecreatively, a waveguide can actually “swap” or “shuffle” light amongfibers. For example, with a two fiber connector will mate with anothertwo fiber connector, light leaving fiber 1 will enter the correspondingfiber in the other half of the connector. Advantageously, by using aconnector created as described herein, a stack of high precision piecescan be used to direct the light leaving fiber 1 into the fiber that doesnot correspond when the connectors are joined. This approach can bereadily extended to multiple fibers in the same connector.

In a further variant, the same process is followed, but the holes areall tapered narrower and narrower in each successively stacked piece(i.e. the openings in the first piece are large and the holes in eachsuccessive piece in the stack tapers smaller and smaller).

This allows, for example, a one-dimensional or two-dimensional array ofoptical devices to be coupled to a one dimensional or two dimensionalarray of optical fibers when the number of optical devices exceeds thenumber of optical fibers and hence it becomes desirable to merge thesignals from several optical devices into a single optical fiber. Thisis useful when redundant devices provide for backup signal capability(i.e. one device can operate as the primary device while the otherscoupled into the fiber can be operated as backup devices). Anotherapplication allows several optical devices, each with its own operatingwavelength, to be combined into a single fiber.

There are at least two ways this can be done. One, shown in FIG. 24, isto create a one-dimensional or two-dimensional array of tapers usingmultiple pieces 2400 which when formed into a waveguide combine thelight from a larger area 2402 on one side and taper it down to a smallerarea 2404 on the other side. On the larger end 2402, the opening of thetapered array pieces can have a diameter large enough to accept lightfrom several optical devices simultaneously.

An alternative variant, shown in FIG. 25, the pieces (only two of which2500, 2502 are shown) are designed to be stacked so as to create a twodimensional array of optical Y branches 2504, 2506 which can combine two(or more) optical signals into single fibers. Depending upon theparticular application, the Y branches can be symmetric, asymmetric ordeveloped in random patterns to provide unique connection topologies.

In yet a further variant, by using different sized holes and offsettingthem from piece to piece in the stack the same technique can be used tocombine multiple waveguides into a single waveguide, for example, forcombining the outputs of several optical devices or coupling multipledevices into an individual optical device.

Note that even more complex connections are possible using a similartechnique, for example, 4 to 1 combining arrangements, shuffling ofindividual fiber outputs, combining of non-next nearest neighbordevices, etc. For example, a stack 906 of pieces from the wafer shown inFIG. 9 (stack shown in cutaway cross section not to scale) creates a 6to 4 to 2 waveguide.

Thus, it should be understood that the technique adds a third dimensionof freedom and thus allows one- or two dimensional arrays of opticaldevices (emitters, detectors, modulators, micro electro mechanicalsystems etc.) to have optical outputs which can be combined, split,routed, and shuffled in an arbitrary manner so that at the output of thestack, signals are output in a specific manner different from the inputto the stack.

In addition, the technique allows for incorporation of other elements,for example, by inserting microlenses 1002 into a high precision piece1004 to create an array of microlenses (FIG. 10B). This can be done by,for example, depositing microlenses in the tapered holes of highprecision pieces such as made in connection with FIG. 13, 14 or 15 or inetched “stepped” holes of two or more different diameters, or dishedholes (since, in either case, ease of fiber insertion is not a concernfor this piece). Once such a piece is created, it can be integrated withother pieces as desired. Similarly, the approach can be used toincorporate diffraction gratings into a stack or a low precision piece.

The techniques described herein can further be used to create a single,high-density connector to connect fiber riser cables together, insteadof through use of huge multi-connector assemblies as is currently done.

In a further variant, by using a high-precision piece made of silicon ina connector used to attach fiber bundles to transceiver modulescontaining optics attached to semiconductor wafers (e.g. a siliconopto-electronic chip), the thermal coefficient of expansion of the piecein the connector can be readily matched with the coefficient ofexpansion of the chip in the module. Thus the connection will notdegrade appreciably due to temperature fluctuations.

Notably, while some variants of the technique described hereinspecifically use a combination of high-precision and low precisioncomponents, the approach is equally applicable to a single grown,molded, milled, or machined piece that can be processed as either alow-precision, a high precision or combination piece.

FIGS. 26A through 26C show a yet a further, more complex, combinationapplication of the techniques described herein. As shown, a microlensarray 2602, such as shown in FIG. 10B is incorporated as one of theelements in the stack 2604 of high precision pieces 2606, 2608. As shownin FIG. 26A, fibers 2610, in this case single mode fibers, are held by acombination of a low precision piece 2612 and the two high precisionpieces 2606, 2608. The microlens array 2602 is stacked with the two highprecision pieces and combined with the low precision piece 2612 tocreate, in this case, a ferrule 2614 compatible with an MTP, MPO, MPX orSMC style connector (FIG. 26B). In this application, the connector isdesigned to be coupled to an optical device array 2616, for example, anarray of transmitters 2618. The microlenses 2620 focus the incidentlight beam more narrowly so that more accurate and/or efficient couplingbetween the optical devices and fibers can be obtained.

Advantageously, assuming that the array of devices was created forcoupling to multimode fibers of a particular pitch, through use of theferrule of FIG. 26B, the same array can be coupled to single mode fiberswithout taking any special action or changing the device array at all.FIG. 26C shows a single optical device 2622 in the array 2618 focussinglight 2624 between the device 2622 and a single mode fiber 2626 throughuse of the arrangement shown in FIGS. 26A and 26B.

FIG. 27 is a photograph of a high precision piece 2700 created asdescribed herein.

FIG. 28 is a photograph of the piece 2700 mounted in a low precisionpiece 2800 as described herein and showing alignment pins 2802 passingthrough the low precision piece 2800 and the piece 2700.

FIG. 29 is a photograph, in ¾ view of a ferrule created according to onevariant of the invention, for use in an MTP connector and superimposedagainst a penny for relative sizing.

FIG. 30 is a photograph of a fully assembled MTP style connector asdescribed herein having at least one high precision piece holding 72light carrying fibers.

Thus, while we have shown and described various examples employing theinvention, it should be understood that the above description is onlyrepresentative of illustrative embodiments. For the convenience of thereader, the above description has focused on a representative sample ofall possible embodiments, a sample that teaches the principles of theinvention. The description has not attempted to exhaustively enumerateall possible variations. That alternate embodiments may not have beenpresented for a specific portion of the invention, or that furtherundescribed alternate embodiments or other combinations of describedportions may be available, is not to be considered a disclaimer of thosealternate embodiments. It can be appreciated that many of thoseundescribed embodiments are within the literal scope of the followingclaims, and others are equivalent.

What is claimed is:
 1. A method of preparing a mating surface and afeature defined by a wall that will mate with the mating surface to aspecified sub-micron tolerance, the method comprising: optimizing thesize of at least one of the mating surface or at least part of the wallby uniform oxidization in a slow, controlled manner over a period ofseveral hours until the specified sub-micron tolerance is achieved.
 2. Amethod of forming a female format connector comprising: coupling atleast one high-precision piece to a low precision piece to form aferrule, the low precision piece comprising a first and second alignmentopenings, the at least one high-precision piece comprising a pluralityof fiber holes, a first and second removable portions, and a third andfourth alignment openings at least in part disposed on the first andsecond removable portions, the first, second, third and fourth alignmentopenings sized and positioned to provide accurate alignment between thehigh-precision piece and the low precision piece during coupling; andmodifying the third and fourth alignment openings after coupling.
 3. Themethod of claim 2 wherein the third and fourth alignment openings beforemodification are cylinders having a cross section of a first diameterand the third and fourth alignment openings after modification arecylinders having a cross section of a second diameter, larger than thefirst diameter.
 4. The method of claim 2 wherein the modifying the thirdand fourth alignment openings comprises changing the shape of the thirdand fourth alignment openings.
 5. The method of claim 2 wherein themodifying the third and fourth alignment openings comprises removing thefirst and second removable portions.
 6. A method of forming a femaleformat connector comprising: aligning a low precision piece and a highprecision piece using a first and second alignment pins passing througha first, second, third and fourth alignment openings in the low and highprecision pieces, the first and second alignment openings being in thelow precision piece, the third and fourth alignment openings being inthe high precision piece and being disposed at least in part on a firstand second removable portions of the high precision piece, the highprecision piece further having multiple fiber holes; bonding the lowprecision piece to the high precision piece to form a ferrule; removingthe first and second alignment pins from the alignment openings afterbonding the low precision piece and high precision piece; and modifyingthe third and fourth alignment openings after aligning the low precisionpiece and high precision piece.
 7. The method of claim 6, wherein thethird and fourth alignment openings are modified after aligning andbonding the low precision piece and high precision piece.
 8. The methodof claim 6, wherein modifying the third and fourth alignment openingscomprises making the third and fourth alignment openings larger.
 9. Themethod of claim 6, wherein modifying the third and fourth alignmentopenings comprises changing the shape of the third and fourth alignmentopenings.
 10. The method of claim 6, wherein modifying the third andfourth alignment openings comprises removing the first and secondremoveable portions to partially remove the third and fourth alignmentopenings from the ferrule.
 11. The method of claim 6, wherein modifyingthe third and fourth alignment openings comprises removing the first andsecond removeable portions to entirely remove the third and fourthalignment openings from the ferrule.